This invention concerns a semiconductor component with at least one pressure sensor and a semiconductor chip having a semiconductor structure for at least one additional function of the semiconductor component and with a casing attached to the semiconductor chip.
Such a semiconductor component is known from R. Frank, xe2x80x9cPressure sensors merge micromachining and microelectronics,xe2x80x9d Sensors and Actuators, A28(2), pp. 93-103 (1991). It has a semiconductor chip in whose substrate is etched a recess from the rear side, thus reducing the wall thickness of the semiconductor chip in some areas. Therefore, in the area of the recess, this yields a membrane of semiconductor material arranged in the surface plane of the semiconductor chip on the front flat side of the semiconductor chip, so that it can be deflected by a pressure acting against the restoring force of the semiconductor material. A measuring bridge arranged on the membrane has wire strain gauges to measure the bending deformation of the membrane caused by the acting pressure. The semiconductor chip also has a semiconductor structure for additional functions of the semiconductor component. This includes a circuit for temperature compensation of the pressure sensor and a microcomputer with a memory and an input/output interface for communication with an external computer.
The previously known semiconductor component has the disadvantage that a relatively large chip area must be reserved on the semiconductor chip for the membrane, thus increasing the cost of manufacturing the semiconductor component. Another disadvantage is that the membrane is under bending stress with the acting pressure, and the bending stresses are propagated into regions of the semiconductor chip near the membrane and can alter the electric properties of the semiconductor structure there. Thus, crystal planes in the structure may undergo mechanical deformation with the pressure acting on the membrane, for example, thus resulting in electric potentials in the semiconductor material which can alter the off-state voltage of pn junctions in the structure, for example. The additional function of the semiconductor chip can thus be impaired or disturbed. Another disadvantage of the semiconductor component is that the semiconductor chip must be masked and etched on the back side to produce the membrane, thus requiring an additional step.
Therefore, an object of the invention is to create a semiconductor component of the type described at the outset, avoiding any impairment of the additional function of the semiconductor component when a pressure acts on the pressure sensor. In addition, the semiconductor component should be inexpensive to manufacture.
This object is achieved in that the semiconductor chip is attached to the casing by an elastic carrier arrangement; the semiconductor chip on the whole can be deflected relative to the casing against the restoring force of the material of the carrier arrangement; and for indirect measurement of a pressure which acts on the semiconductor chip and produces a deflection, at least one position sensor that works together with the semiconductor chip is provided.
The semiconductor chip is thus deflected relative to the casing when pressure acts on it on the whole, thus preventing any change in its geometric dimensions. This avoids mechanical stress on the semiconductor chip and the development of bending stresses or tensile stresses and a related electric influence on the semiconductor structure provided for the additional function. Thus, the additional function can be executed with greater precision, while on the other hand the semiconductor component also has greater operational reliability, which permits its use in a larger temperature range, for example. Since this eliminates a membrane integrated into the semiconductor chip, it also results in a much smaller chip area, which permits inexpensive manufacture of the semiconductor chip. For example, the position sensor provided for indirect measurement of the pressure producing the deflection of the semiconductor chip may be an optical, inductive or magnetic sensor, preferably a non-contact sensor, which may optionally be integrated partially or completely into the semiconductor chip.
An especially advantageous embodiment of the invention provides for the position sensor to have a capacitor with at least two electrodes, one of which is a component of the semiconductor chip and the other is arranged on the casing. The capacitance of the capacitor is inversely proportional to the distance between the two electrodes. The deflection of the semiconductor chip depends on the spring characteristic of the carrier arrangement and may be in linear relationship to the pressure acting on the carrier arrangement and/or the semiconductor chip, for example. The capacitance is then inversely proportional to the pressure. The capacitive position measurement permits an especially simple design of the semiconductor component, where one of the capacitor electrodes may be formed by an electrically conducting area of the casing, for example, and the other capacitor electrode may be formed by an electrically conducting layer on the semiconductor chip and/or by the substrate of the semiconductor.
It is advantageous if the carrier arrangement has printed electric conductors for connecting terminal contacts arranged on the casing to terminal points on the semiconductor chip. The power supply voltage for the semiconductor chip, electric control signals and/or measurement signals can be transmitted easily between the semiconductor chip and the terminal contacts on the casing. The conductors may be printed on the carrier arrangement, for example, permitting inexpensive manufacture of the carrier arrangement. The capacitor electrode on the casing may optionally also be connected to the structure on the semiconductor chip, which may include a control and/or analysis device, by one of the printed conductors.
An especially advantageous embodiment of this invention provides for the printed conductors to be connected to the terminal points of the semiconductor chip and/or the terminal contacts of the casing by means of flip-chip technology. Bumps may be provided for electric contacting at the terminal points on the semiconductor chip and/or the printed conductors of the carrier arrangement. They may be soldered to mating contacts provided for them, for example, or connected by some other means. At the connecting points designed in the flip-chip technology, a plastic compound with conductive particles embedded in it may also be arranged between the printed conductors and the terminal points on the semiconductor chip or the terminal contacts of the casing, providing an electric connection between the printed conductors and the terminal points or terminal contacts. Bond wires between contact points to be joined can be eliminated by the flip-chip technology, thus greatly simplifying assembly of the semiconductor component.
A preferred embodiment of this invention provides for the carrier arrangement to have at least one substrate that carries the semiconductor chip and is elastically flexible against the restoring force of its material, for the substrate to be designed preferably as a bridge, with opposite end areas acting on the casing, and for the semiconductor chip to be fixedly connected to the substrate in the course between these two end areas. This yields a largely symmetrical carrier arrangement, which causes an approximately parallel displacement of the semiconductor chip and any capacitor electrode arranged on it, when acted upon by the pressure to be measured.
One embodiment of this invention provides for the substrate to be a film, in particular a plastic film. This may be made, for example, of polyimide, polyethylene or polyvinyl chloride. The film is applied to the casing, preferably on its peripheral edge, and is clamped there. The substrate is preferably arranged in the middle between opposite edge areas of the film acting on the casing, where it is fixedly bonded to the film.
It is advantageous if the substrate has a reduced material cross section at least in some of the intermediate area between the semiconductor chip and the casing. To that end, the substrate may have a wall area with perforations and/or a reduced thickness, for example. This yields a greater elasticity in some areas, so that low pressures can be measured better.
In an advantageous embodiment of this invention, the semiconductor chip has at least one structure designed as a sensor, with the substrate having at least one through-hole and the semiconductor chip with the sensor surface facing the through-hole attached to the substrate. The through-hole and the semiconductor chip then border a specimen container in which a medium to be tested can be arranged. To test this medium, the semiconductor chip may have, for example, a chemical, optical and/or magnetic sensor. A culture medium containing living biological cells may be arranged in the specimen container. The cells may optionally be adherent to the sensor surface of the semiconductor chip so that electric signals on the cells can be measured with the sensor. The specimen space bordered by the through-hole and the semiconductor chip may be connected to a pump for replacing the culture medium. Then the pressure induced by the pump in the specimen container, which can lead to changes in the electric signals by the biological cells, can be measured directly with the pressure sensor in the semiconductor component. The pressure in the specimen container may then optionally be taken into account in analysis of the signals measured on the cells.
A gasket surrounding the through-hole is preferably arranged between the substrate and the semiconductor chip, in particular between the active sensor surface and the terminal points of the semiconductor chip. A chemically aggressive medium in the specimen container formed by the through-hole can thus be kept away from the terminal points of the semiconductor chip. This prevents corrosion at the terminal points.
It is advantageous if a gap, in particular a capillary gap, is formed between the semiconductor chip and the substrate, and if a plastic potting compound is poured into this gap. The gap can then be filled with the plastic potting compound in a simple manner by the underfill technique during manufacture of the semiconductor component. The plastic potting compound is preferably added to the capillary gap from the side of the substrate facing the semiconductor chip to prevent contact between the plastic potting compound and the active sensor surface in the area of the through-hole.
An advantageous embodiment of this invention provides for the semiconductor chip to be arranged in a receptacle recess in the casing, and for the substrate to cover the opening of the receptacle recess and to be attached at its peripheral edge to the edge area of the casing bordering the receptacle recess. The receptacle recess may be formed, for example, by the cavity of a conventional standard-IC-casing, or it may be cut into a circuit board, preferably having multiple layers. It is even possible for the bottom of the receptacle recess to form a stop for the semiconductor chip on which the semiconductor chip is supported, its back side facing away from the active sensor surface, when there is a pressure in excess of the measurement range of the pressure sensor. The pressure sensor of the semiconductor component therefore has a high pressure strength. Furthermore, in the receptacle recess the semiconductor chip is also protected from mechanical damage.
It is especially advantageous if the elastic carrier arrangement and semiconductor chip form a replaceable sub-assembly, if there are pressure contacts connected to the printed electric conductors on the carrier arrangement, working together with the terminal contacts of the casing in the use position, and if clamping means are provided for securing the sub-assembly in the use position. The sub-assembly having the semiconductor chip with the pressure sensor and the active sensor surface can then be replaced easily in a laboratory, for example.
An especially advantageous embodiment of the invention provides for the casing to have an installation port for the sub-assembly, for the casing to be detachably connectable to the installation port with a connecting part having at least one inlet opening and one outlet opening for a medium to be tested, for the pressure contacts to be arranged on the back side of the substrate facing away from the connecting part when the sub-assembly is inserted into the installation port and to be supported there against the terminal contacts of the casing, and for the front side of the substrate facing the connecting part to be acted upon by pressure either directly or indirectly through a gasket surrounding the through-hole of the substrate. With the subassembly inserted into the receptacle recess of the casing part behind the installation port so that it is in use position, the connection part acts on one of the flat sides of the elastic substrate, preferably designed as a film, directly or indirectly by way of a gasket or the like, and the terminal contacts of the casing in the receptacle recess also act on the other flat side of the substrate.
The substrate is clamped between the connecting part and the casing having the receptacle recess, so that the pressure contacts of the substrate connected to the printed conductors are pressed by the restoring force of the elastic substrate material on the terminal contacts of the casing assigned to them. Due to the elasticity of the substrate material, the pressure contacts are pressed especially uniformly and with a constant pressure against the mating contacts. This yields a good long-term stability of the electric connections between the pressure contacts and the mating contacts. The connecting part having the inlet and outlet opening, connectable to the installation port of the casing may be part of a pump casing of a pump for supplying or circulating a medium to be tested.